A microprocessor-controlled programmable thermostat has become a popular "after-market" device to control a residential heating and air conditioning system. However, such a thermostat is often incompatible with the electronic module in the heating and air conditioning system. The compatibility problem is usually caused by the solid state switch, called a "triac", used by the programmable thermostat. The triac usually does not break sufficiently "clean".
One way to solve the compatibility problem is to use a pulse snap action relay instead of a triac. A pulse from a microprocessor switches the relay from an "on" position to an "off" position, or from "off" to "on". This relay makes contact and breaks contact cleaner than a triac. However, a pulse snap action relay has the problem that sometimes spurious signals in the power lines or even radio signals can cause the relay to change its on-off position.
The system of the present invention solves the above-noted and other problems of the prior art by providing a method and apparatus for monitoring and correcting the position of the contacts of a relay. The invention features the capability of continually monitoring the position of the thermostat's relay.
The invention provides an air temperature control system which includes a thermostat and a relay conductively coupled to the thermostat. The relay has a contact or contacts. The system further includes a programmable monitor conductively coupled to the contact and to the thermostat for continually determining the position of the contact, and adjusting the position, as needed, to be in conformance with a predetermined position stored in the monitor. In another feature of the invention, the thermostat is a microprocessor-controlled programmable thermostat. In another feature of the invention, the monitor has a memory containing predetermined positions for the contact. In still another feature of the invention, the relay is a snap action pulse relay.